The objective of this work will be to test the hypothesis that H plus ions produced by the electron transport reactions, interact with energy transducing organelle membranes via specific subcompartments within the membrane. Two lines of recent independent experiments from this laboratory suggest that the membrane has domains, probably containing fixed charge groups, that specifically receive protons from one or the other of the proton translocating redox reactions, and can process them into the ATP formation mechanism before they equilibrate with the inner osmotic space. The methods to be used include searching for conditions that give evidence for protons entering the ATP formation mechanism from one or another of the postulated intramembrane pools or subcompartments, as well as from the inner osmotic space. Using chemical modification reagents as probes, evidence indicates that a membrane component of the energy coupling complex specifically interacts with protons released in photosystem II water oxidation. Amino acid sequence determination of the protein will be used to identify the residues involved in the interaction.